In various complex electronic systems, it is desirable to repair a working system or change the configuration of the system without interrupting the operation of the system. To this end, various components or peripherals of the system may be configured to be hot-swappable. What this means is that these various components or peripherals may be removed and installed while the rest of the system is still operational. This may occur, for example, in systems such as large computer servers or cloud storage systems that need to remain operational even during times when the system needs to be maintained or repaired.
Hot-swappable components are configured to be inserted and removed in fully operational systems in which power is applied. In order to support the ability to insert and remove these components from a live power supply, each hot-swappable component typically includes power supply protection circuitry that prevents damage to the components of the component or peripheral, and allows for the orderly startup and shutdown of the hot-swappable component or peripheral.
One of the issues encountered in the design of hot-swappable components is effectively dealing with the issue of inrush current. In many situations, the power supply bus of the hot-swappable component includes a very large amount of capacitance. When this high capacitance component is plugged in to the system, a very large amount of current may flow in order to initially charge the large capacitance. In many hot-swappable systems, this inrush current is controlled by including a series element that provides resistance and or controls the flow of current when the hot-swappable component is initially plugged into the system. Such a series element may be implemented for example using a power transistor such as a power MOSFET that is initially configured to have a high resistance during startup and then transitions to a much lower resistance during operation.
In order to deal with very large amounts of current power, MOSFETs that are used as series elements and hot-swappable components are generally very large in order to make sure that inrush currents do not exceed the power MOSFET's ability to handle currents. However, it is not uncommon for such power MOSFETs to fail in the field due to inrush currents being over the maximum amount that can be handled by the device, or fail due to the temperature of the device being over its thermal limit.